Method of opening chrome ore

Abstract

Disclosed is a method of opening iron oxide-chromic oxide ores of trivalent chromium by contacting the ore with an aqueous alkali metal hypochlorite bleach and recovering a liquid containing hexavalent chromium from the reaction media. The hexavalent chromium produced by the bleaching action is normally in the form of alkali metal chromate. According to a preferred exemplification, the alkali metal chromate is electrolytically converted to an alkali metal dichromate.

I claim: 
     
       1. A method of opening FeO.Cr 2  O 3  ore comprising the steps of: contacting the ore with an aqueous alkali metal hypochlorite solution below the boiling point of said solution whereby to form an aqueous acidic slurry; and   recovering a liquid containing hexavalent chromium from said aqueous slurry.   
     
     
       2. The method of claim 1 comprising recovering a solid containing trivalent iron from said aqueous slurry. 
     
     
       3. The method of claim 2 comprising contacting the ore with aqueous alkali metal hypochlorite solution, separating the solids from the liquid and thereafter contacting the solids with aqueous alkali metal hypochlorite solution. 
     
     
       4. The method of claim 1 comprising adjusting the pH of the aqueous slurry to at least pH=10 after opening the ore whereby to render said slurry alkaline and thereafter recovering a liquid from said aqueous slurry. 
     
     
       5. The method of claim 4 comprising adding alkali metal hydroxide to the aqueous slurry. 
     
     
       6. The method of claim 1 comprising contacting the ore with from about 2.5 to about 3.2 moles of alkali metal hypochlorite per mole of chromium and thereafter recovering a liquid from said aqueous slurry. 
     
     
       7. The method of claim 1 comprising feeding the liquid containing hexavalent chromium to an anolyte chamber of an electrolytic cell, feeding water to a catholyte chamber of the cell, passing an electrical current through the cell, recovering hydrogen and alkali metal hydroxide from the catholyte chamber of the cell, and recovering chlorine and alkali metal dichromate from the anolyte chamber of the cell. 
     
     
       8. The method of claim 7 comprising contacting alkali metal hydroxide and chlorine from said electrolytic cell whereby to form aqueous alkali metal hypochlorite solution and thereafter contacting FeO.Cr 2  O 3  ore with the aqueous alkali metal hypochlorite solution formed thereby. 
     
     
       9. A method of opening FeO.Cr 2  O 3  ore comprising the steps of: contacting ore particles with an aqueous alkali metal hypochlorite solution below the boiling point of said solution whereby to form a slurry of ore particles and bleach;   thereafter adjusting the pH of the slurry to at least pH=10;   filtering the pH adjusted slurry whereby to separate iron rich solids from an alkali metal chromate-alkali metal chloride liquid;   feeding the alkali metal chromate-alkali metal chloride liquid to an anolyte chamber of an electrolytic cell, feeding water to a catholyte chamber of the electrolytic cell, passing an electrical current through the electrolytic cell, recovering hydrogen and alkali metal hydroxide from the catholyte chamber of the cell, and recovering chlorine and alkali metal dichromate from the anolyte chamber of the cell;   contacting alkali metal hydroxide and chlorine from said cell whereby to form aqueous alkali metal hypochlorite solution; and   thereafter contacting FeO.Cr 2  O 3  ore with said aqueous alkali metal hypochlorite solution.   
     
     
       10. The method of claim 9 comprising contacting the ore with aqueous alkali metal hypochlorite solution whereby to form said slurry, separating the liquid from the solid, and therafter contacting the solid with aqueous alkali metal hypochlorite solution. 
     
     
       11. The method of claim 9 comprising contacting the ore with from about 2.5 to about 3.2 moles of alkali metal hypochlorite solution per mole of chromium. 
     
     
       12. A method of opening FeO.Cr 2  O 3  ore comprising the steps of: contacting ore particles with an aqueous alkali metal hypochlorite solution below the boiling point of said solution whereby to form an acidic slurry of ore particles and aqueous alkali metal hypochlorite solution:   thereafter adjusting the pH of the slurry to at least ph=10;   filtering the pH adjusted slurry whereby to separate iron rich solids from an alkali metal chromate-alkali metal chloride liquid; and   feeding the alkali metal chromate-alkali metal chloride liquid to an anolyte chamber of an electrolytic cell, feeding water to a catholyte chamber of the electrolytic cell, passing an electrical current through the electrolytic cell, recovering hydrogen and alkali metal hydroxide from the catholyte chamber of the cell, and recovering chlorine and alkali metal dichromate from the anolyte chamber of the cell.